Hi, bhaisahab.
1. Nick is the nickname of Nicholas.
Specific person called Nicholas.
3. Nick is the nickname for Nicholas.
The usual nickname for a person called Nicholas.
6. Nick is a nickname for Nicholas.
One of the nicknames for a person called Nicholas, 'Nicky' and 'Nicko' exist as alternatives.
________
Please check the following statements and a question.
1. Bob (Joe, Dick,Bill...etc.) is the nickname of Nicholas. --- possible
3. Bob (Joe, Dick,Bill...etc.) is the nickname for Nicholas. ---- incorrect statement.
6. Bob (Joe, Dick,Bill...etc.) is a nickname of Nicholas. ---- incorrect statement.
3+. Nick is the nickname for Nicholas.
Is it similar to 'Nick is short (or diminutive) for Nicholas?
Thanks